Once again, the system doesn’t make up the inputs itself, it executes them from input of PF (AP) and in ALT LAW in such a manner it would not hinder PF to recover A/C from the upset.
Hmmm, doesn't the A/C makes inputs of its own in ALT law, trimming the THS ? Sure, this was due to strange PF inputs but was he really aware of the move ?
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The actual logic inside the FCPC is not open to the public, so we have to rely on what is stated in the released documents.
"Pitch:
The side sticks and in some cases the pitch trim control wheels control the aircraft in pitch.
They act on the elevators and on the THS depending on the different laws.
1. Nz law.
This FCPC law is the normal pitch law engaged during the flight phase.
The pilot commands a load factor via a pitch action on the side stick.
The Nz law executes this command, depending on the aircraft feedbacks, so that:
- the short-term orders are executed by the elevator servo controls.
- the long-term orders are executed by the THS actuator (autotrim function).
The gains depend on Vc, on the flap and slat position and on the CG position."
From study material and answer to
Machinebird's question:
"An override mechanism, which is installed in the PTA
(Pitch Trim Actuator),
makes sure that the mechanical control through the trim wheels cancels the electrical control.
When a manual command is made with the trim wheels, the override
mechanism gives priority over the electrical command from the FCPCs.
It mechanically disconnects the PTAoutput from the mechanical input(via
electro-magnetic clutch) and also operates the overriding detection
switches which in turn signal the FCPC's to stop any electrical command
from the FCPC's."
It's not stated but it seems logical that when a manual pitch trim wheel
command is made or an autotrim command is cancelled by holding the
manual trim wheels (THS runaway) the side stick should be released to neutral.
In that case there is no SS input anymore and when manual input on Trim wheel stops also,
the electro-magnetic clutch is released again and THS system is ready to
take new SS orders.
Cryptic schematic but could not find any better:
Don't you agree that even without pilot input the THS would trim up once the A/C is stalled ?
In ALT 2: The HI AOA Protection is lost, in case of a dual ADR failure (or ADR DISAGREE).